This invention relates generally to domestic washing machines and more particularly to a drive system for agitating and spinning appropriate elements of the washing machine.
Conventional washing machines typically include a perforated basket for holding clothing or other articles to be washed, an agitator disposed within the basket which agitates the clothes in the basket, and a motor which drives the agitator and the basket. The articles to be washed are immersed in water with detergent and washed under the influence of an oscillating agitator. After agitation, the articles are rinsed with clean water and the basket is spun at high speed to centrifugally extract the rinse water from the articles. Typically, a mechanical drive system produces the oscillatory motion of the agitator upon rotation of a drive motor in one direction, and produces continuous rotation of the basket upon rotation of the drive motor in the other direction.
U.S. Pat. No. 5,605,212, issued Feb. 25, 1997 to Hans Hauser, is exemplary of such a drive system. The Hauser patent discloses a drive system including a bi-directional motor that can reverse its rotation direction to achieve different modes in the wash cycle. The motor rotates in a first direction during the agitate mode and in a second direction, opposite the first direction, during the spin mode. A transmission is provided with gears to convert the rotary motion of the motor into oscillatory motion of the agitator during agitation; during the spin mode, the transmission transfers motor rotation to the basket. The Hauser drive system further includes a spring loaded clutch/brake mechanism that holds the basket immobile during agitation mode. This mechanism uses a ball and hub assembly to engage or disengage the brake. The ball and hub assembly includes two rotatively mounted hubs having a plurality of ball bearings disposed therebetween in inclined races. The uppermost of the two hubs supports a spring loaded brake disk. When in the agitation mode, the balls remain at the bottom of the inclined races and the brake disk is biased into contact with a stationary brake drum, so that the brake is locked. When the wash cycle calls for the spin mode, the direction of motor rotation is reversed. This causes the balls to run up the inclined races, lifting the uppermost hub and the brake disk, thereby unlocking the brake. With the brake released, the transmission transfers motor rotation to the basket, resulting in the desired spinning of the basket.
Although generally operating in a satisfactory manner, this type of drive system suffers from a potential drawback in that the ball bearings are most highly loaded when the dynamic loading conditions are the worst, i.e., during spin mode. As the basket approaches its terminal speed during spin mode, the accelerating torques diminish and the brake spring force starts to force the balls back down their races. This causes the brake disk to descend until the disk tags the drum, increasing the torque, reversing the process, and re-releasing the brake. Tagging repeats over and over so that small motion of the highly loaded balls up and down the races can be stimulated, a condition that can produce fretting wear of the ball races. If the fretting becomes severe, a detent large enough to inhibit free ball rolling can develop and lead to possible brake failure. Furthermore, uneven distribution of wet clothes in the basket can aggravate the problem because large unbalanced loads during spin can concentrate the load onto one or two of the balls instead of being shared equally among the balls.
Accordingly, there is a need for an improved washing machine drive system in which the ball bearings are not loaded during the spin mode, thereby eliminating tagging and severe fretting conditions.